Reenforced concrete pipe



Nov. 18, 1930. w. c. ARMLEY 1,781,599

REENFORCED CONCRETE PIPE Filed May 7, 1927 wuemtoz UNITED STATESPATENT-.- OFFICE WALTER C. PAIRMLEY, OF UPPER MON'ICLAIR, NEW JERSEYnnn'uroncnn CONCRETE PIPE Application -fi1ed May 7, 1927. Serial No.189,613.

This invention relates to a method and means for reenforcing concretestructures, such as conduit pipes, etc., and has for its primary objectto provide reenforcing means around the pipes which will materiallylessen the tendency of longitudinal cracking of the concrete of whichthe pipes are constructed.

A further object of the invention is to arrange the reenforcing means insuch a manner that the tensile stresses caused by the application of aload upon jthepipes will be sustained by the reenforcing means therebypreventing stressing of the concrete pipes beyond their proper limits.

Another object of the present invention is to permit a predeterminedamount of initial compression to be placed within the concrete structureof the pipes particularly at those points which will later be placedunder tensile stresses due to the application of a load so that theconcrete structure will not be under tension at all, or at least to onlya very small degree.

A still further object of the invention is to providereenforcing meansabout the concrete pipes, which will be substantially free in movementwith respect to the concrete by which it is supported so that stressescreated in the reenforcing means by the application of a load to thepipe sections will be distributed substantially equally throughout thereenforcing means.

Another object of the inventionis to provide adjustable reenforcingmeans for the concrete pipe sections so that by proper ad-' justment theconcrete will be placed under ini- 'tial compression and the reenforcingmeans =under initial tension so that the compression in the concreteacts oppositely to the effect produced by internal pressure or bytension moments from external loads and results in greatly strengtheningthe concrete pipe sections.

With the object above indicated and other of a section of concrete pipeshowing the arrangement of the reenforcing means;

Fig. 2 is a transverse cross sectional view taken on line 2 2 of Fig. 1,and showing the fidjusting means for the reenforcing memers;

Fig. 3 is a transverse cross sectional View of a modified arrangement;and

Fig. 4 is a transverse cross sectional view taken on the line 4-4 ofFig. 3.

The general method of manufacture of concrete pipes has been to embed inthe molded concrete forming the walls of the pipes a skeleton ofreenforcing steel, of mesh or rod type. When the concrete hardens thereenforcement becomes firmly embedded in the concrete. The fundamentalprinciples underlying reenforced' concrete in general are two: 1st, thenearly equal expansion and contraction of the two materials caused bychanges of temperature which permits reasonable team work between thetwo and, 2nd, the fact that there is a great adhesion between theconcrete and the reenforcement, thus permitting the reenforcing steel toexert its superior strength most efliciently in reenforcing the concreteat those points where the latter is subjected to the greatest tensilestresses. i

In reenforced concrete pipe work certain, methods as now practiced areobjectionable and it is the purpose of this invention to minimize orwholly avoid these objections. 1

place with practically no internal stress being set up within the massof the concrete. The resulting pipe will therefore, when subjected tobending stresses of loading, be able to withstand these stresses up tothe normal limit of the tensile strength of the concrete.

The modulus of the concrete in tension therefore, usually runs two orthree hundred pounds per sq. in. and it is this transverse sult that thesteel becomes subjected to a can tain amount of initial compression andthe concrete to a corresponding initial tension.

This adverse effect of the reeinforcement frequently causes longitudinalcracking of pipes, the tension in the concrete being in excess of itstensile strength. Whether the pipe actually cracks or not before it issubjected tointernal or external loading is more or less immeterialsince the first effect of the steel reenforcement is to produce aninitial tension in the concrete and cause it to crack at an earlierstage than it would otherwise have done. Furthermore, the cracks whenthey do occur under loads will be wider than they would be if thereenforcement had not been-in a state of initial compression, and thesteel under loading stresses will not actually be stressed up to thelimits which are calculated to be its working limits.

Another gain which the invention accomplishes is that it permits acertain amount of initial compression to be put into the concreteparticularly at those points where subsequently the concrete will beunder tensile stresses. This initial compression will be such amountthat ultimately the concrete will be relatively in tension to only asmall degree or not at all. It furthermore makes it possible to producea structure in which the concrete can be stressed up to its fullcompressive stren h with very little or no tension upon t e tension sideof the section,

I or, in fact with the entire section of the pipe actually still incompression when the latter is withstanding a considerable bendingmoment or stress from external loads or internal pressure. It also makesit possible to stress the reenforcement up to any desired degree and thehigher the limits the less will be the tendency for the concrete tocrack on the tension side of the pipe section.

There can be no question that any process,

manipulation or design which lessens the tendency of concrete to crackis an improvement of the first importance over-present practice inreenforced concrete construction, especially since at present it is notexpected that the tension in-the reenforcement shall exceed about threeto five thousand pounds per square inch before the concrete actuallycracks. Under hydrostatic pressuremuch of I coming carrie crete may bedue to leakage through minute cracks that escape detection of the eye.In fact, it has been known for many years that concrete may be ru turedand water under pressure may pass t rough althou h the extension is onlyone third or less 0 that nec essary to produce visible cracking. Hereinlies a most fundamental weakness of present practice in reenforcedconcrete particularly when applied to structures sustainin hydrostaticpressures. The methods out ined in this invention are ca able ofentirely over these defects in practice as generally. out at the presenttime.

When a hoop is placed about a pipe 10 as indicated b 11 in. Fig. 1,either around the outside of t e pipe or embedded more or less deeply inthe pipe, the hoop when brought into mitial tension by some means. suchas a saddle 12 through which the ends of the hoop extend and which areheld tight by nuts 13, or by othermeans, it subjects the con crete ofthe entire pipe to compression, the intensity of which is a maximum atthe inner surface of the pipe and decreases according to a certain lawto a minimum at the outer surface of the pipe. This compression in theconcrete acts opposite to the effect produced either by internal waterpressure or by tension moments from external loads. The pipe thereforeis greatly strengthened by the laws sure of the hoop.

ing a circular structure such as a pipe, a bar rel, etc? is not new, butwhat I do claim is that by the performance of certain things inconnection therewith I do produce an entirely new and novel eflfect.

Suppose, for instance, that a hoop with initial tension encircles thepipe 10 as shown at 11 in Figs. 1 and 2. If the hoop is embedded in theconcrete in the ordinary manner, or in a groove 14 about the exterior ofthe pipe and the groove filled with cement mortar 15the hoop becomescement bound in the concrete. It thus ceases to act in the manner of anordinary barrel hoop and becomes reenforcement in the pipe and actsaccording to the laws of reenforced concrete.

Suppose now that the pipe, lying in a horizontal position, is subjectedto a vertical load at the top. The load produces tension effects uponthe inner surface of the pipe at the top and bottom and on the outsideat the horizontal points. It therefore tends to increase theinitialtension of the hoop at the springing lines and to decrease it at the topand bottom. At the top and bottom a point will be reached as the load isincreased where the compression on the outside of the pipe will exactlyneutralize the initial tension in the hoop. With any further addition ofload the hoop, at the top and bottom will cease entirely to act in themanner of a barrel hoop but will begin to sustain compression at anintensity of the same number of times the unit compression in theconcrete, that the modulus of the steel is reater than the modulus ofthe concrete. t the same time the original compression in the intradosalportions of the ring at the top and bottom caused by the originaltension in the hoop will be neutralized by the tension induced by theload. The tension in the concrete therefore will be less than it wouldhave been if there had been no hooping, by the amount of the compressionin the concrete which was caused by the hoop tension.

At the springing lines the conditions will be exactly reversed. That is,the tension in the extrados of the ring will be added to the hooptensionand the compression in the intrados of the section will be addedto that .caused by the initial hoop tension. The effect therefore of thehoop is entirely different from what is experienced in the case of anordinary barrel hoop or similar cases of hooping in wood stave pipes,tanks, etc.

Again, consider the hoop as shown at 11" in Fig. 3. If this hoop isgiven initial tension and then cement bound in the mortar 15 of theconcrete, its action against the effects of external loads will be quitedifferent from that described in the former case. That is to say: whileat the springing line the effect will be as heretofore described, at thetop and bottom the loading compression on the outside of the pipe willbe added to the initial compression in the pipe caused by the initialtension in the hoop, and on the inside of the pipe section the originaltension in the hoop will be increased by the tension increment inducedby the load. With the hoop in this position it will ,act in the samedirection throughout as the loading tensions in the pipe, and thesetensions in the concrete will induce an additional tension in the hoopthroughout all thoseportions of the pipe section where tension isproduced by load.

In order to give the hoop initial tension it is necessary that theconcrete of the pipe shall have sufiicient hardness and compressivestrength to withstand the reaction of the hoop. The means whereby thisinitial tension is induced is similar to that shown in Fig. 2. The endsof the hoop 11 extend through suitable openings in a saddle 12 and aredrawn tightly about the pipe by nuts 13, such as is commonly used onwood-stave pipes, tanks, etc. or by any other means such as electricwelding after the rods have been pulled to a predetermined tension.Suitable grooves 14 are cast in the pipe and it then becomes possible toapply the hoops within the grooves after the pipes have attained acertain amount of curing and hardness and the hoops given an arbitraryamount of initial tension desired. These grooves can be 'molded in theexterior surface of the pipe and be of variable depths, according to therequirements.

There are also conditions when it is not desirable to have the hoopingcement bound but to have it embedded in grooves and fully covered withcement for protection against the elements, or to have it cast directlyin the concrete mass. Suppose a hoop embedded in a groove shown at 14 or14: but with the hoop protected with some suitable material such asasphalt, grease, paper or other means, so that it will remain free toslip within the body of the concrete when fully embedded.

Its, effect in combination with loads will be} quitedifierent from thatof the hoop when cement bound, as discussed above.

If the original hoop 11 is normally circular in position and is thensubjected to the stresses caused by a slight flattening of the pipeunder-load, the hoop will cease to be circular inform but will bechanged into substantially an ellipse. With the hoop free to slip withinthe mass of the concrete its total length will be altered by a veryslight amount only, if the deflection of the pipe is within the usuallimits. The result is that the tension in the hoop will remain unchangedor will be only very slightly increased with the application of theload. Furthermore, the intensity of the tension will be practicallyconstant .throughout the entire length of the hoop. The effect thereforeat the crown will be to add to the compression in the concrete at theextrados of the pipe and add to the compression of the pipe at thespringing lines, by an amount due to the initial tension in the rod. Incase the tension in the intrados at the top and bottom due to the loadis exactly equal to the compression induced in the same regions by theinitial tension in the hoop there will be no tension in the concrete andthe combined effect will be the same as when a load is applied normallyto a section of an arch at the limit of the middle third. With anyfurther addition of load the tension will remain practically constant inthe hoop instead of passing from a zero tension into compression as inthe case above. Any further resistance to the load must thenceforward besustained entirely by the tensile strength of the concrete in theintrados orby other reinforcement introduced for that purpose.

Consider now the case of the hoop shown 'at 11 in Fig. 4 and with thecondition that the hoop is free to slide within the grooves of theconcrete. It was noted above that when a load is applied to the pipe andthe hoop is cement bound a variable tension incrementis added to thatalready existing in the hoop, the intensity of this added tension beinga maximum at the top and bottom and near a maximum at the sides, anddecreasing in either direction from these points to zero tensions in theintermediate regions. On

the other hand, when the hoop is free to slide within the grooves of,the concrete pipe, with the application of load as described, there willbe an equalization of the tension increments due to the load so that theactual tension in the hoop will be nearly constant throughout its entirelength. There is also this further difference which distinguishes thebehavior of this hoop from the one in cirtical to begin with. With anyange. in shape of the 1pipe due to application of a load, the ellipticashaped hoop will become more flattened. It therefore will not remain ofnearly constant length as in the case where it was circular in form, butwith each added increment of deflection an appreciable and increasinglylarge increment will be'added to the length of the hoop.

- From the above discussion it becomes aparent that each of thepositions for reenorcement and manner of embedment de-- scribed has itsuses and particular suitability to add this .reenforcement, for it isplain that certain portions of the ring otherwise would not besufliciently well protected by the presence of the reenforcement. Thissecondar reen orcement may be of any kind desire rods or mesh or otherform. Just how it would act in one tratefits use in com ination withhooping.

Take the case where the hoop'is normally circular, as shown at 11 inFig. 2. As stated above the hoop tension brings all the fibers of thepipe into a certain amount of compression, the intensity being greatestat the inside and gradually decreasing according to a certain curved lawto a lesser amount at the outside. It was shown that when-the tensionefiect of a load at the top: of the pipe becomes equal and opposite tothe induced compression effect of the hoop there is neither compressionnor tension in the inner portion of the-section. Now any furtherincrease in loading would bring tension increments to bear upon theseinner portions of the concrete. If no reinforcement were provided tocounteract these tension increments this part of the section of the pipefrom this point on would act in efiectlike a plain non-reinforcedconcrete ipe, and the ultimate strength would epend upon the tensilecular form, and that is thatthis hoo is elliparticular case will illus-Y strength of the concrete at this point. If, on theother hand, somereinforcement is provided for this portion, the final tension incrementsof the load will be taken up partially or wholly by this addedreinforcement and they will not be thrown entirel into the unprotectedconcrete. A further ustification for this procedure may be cited in thefact which can be shown that the larger the amount of reenforcementthere is in the section, it this steel is embedded in the concrete inthe usual way, the greater will be the tendency for the concrete tocrack from shrinka e. With a relatively smaller amount of reen rcementat this point the tendency to initial cracking of the pipe will beconsiderably reduced.

From the positions of the reenforcement as shown at 11' and 16, it isevident that a style of reenforcement shown in Fig. 4 would notbe'appropriate if the pi e were turned or laid so that the regions 0maximum tensions did not come' where the hooping is placed, butproviding the pipe is so placed, the reenforcement when'in the positionshown in Fig. 4 will be more'efiective than it would be if it wereplaced in the normally circular form as shown in Fig. 2. On the otherhand, the pipe shown in Fig. 2 has the advantage of being suitable forlaying in any position irrespective to the directions of the principalforces. The question as to which or what form of reenforcement describedshould be used will depend upon the special conditions to be met.'-

The same effects as described can be duplicated if instead of placingthe hoopin in grooves of uniform or varying depthsfli the pipes arefirst cast of less than full thickness. The hooping then can be addedwith the intention of having it either cement bound or not cement boundas the case may be, after which an additional thickness can'be castabout the reenforcement, embedding the same and bringing the totalthickness to the required amount. The provision which has been made forlaying the hoops in grooves and then filling. them with mortar is therefore one of expediency and not necessity.

Figs. 2 and 4 show hoops embedded in groves of various depths molded inthe body ofthe pipe. If it is desired to have the hoops embedded inprotective coverings so as to permit their slipping within the body ofthe concrete, the molding of grooves in the exterior of the pipe, orother method described above, is not necessary. If the rods be properlycovered with suitable rotective material, as heavy greases, etc. wit theends lapped and tied and laced so that the lie immediately inside of theouter wall 0 the pipe and inside of the outer shell of the pipe mold,the concrete can then be inserted within the mold in the ordinary wayand the pipe finished in the usual manner. When theniold is removed fromthe pipe and the concrete has been given time to acquire the requiredamount of hardening the threaded ends of the rods can be pulled out andthe saddle 12 or other form of coupling, applied. The nuts 13 can now beturned tightly against the saddle and the hoop 11 pulled up to anydesired amount of unit tension. The hoop being coated, as described,permits it to slip through the concrete and the entire circumference ofthe hoop brought into uniform tension. This action would not be possibleif the hoops were embedded in the ordinary manner and allowed to becomecement bound in the concrete.

While I have illustrated the preferred structure embodying the invention1t is to be understood that other methods of producing the same resultmay be resorted to without departing from the spirit of the invention asdefined in the appended claims.

I-Iaving'thus described my invention what I claim is:

1. A concrete pipe section having a plu rality of grooves extendingcircumferential ly of said pipe, reenforcing means disposed in saidgrooves under tension and adapted to create an initial compression insaid pipe, means for sealing said reenforcing means within said grooves,and means for preventing adhesion between said reenforcing means andsaid sealing means.

2. A concrete pipe provided with grooves,

tension rods insaid grooves adapted to create an initial compression insaid pipe, cementitious material in said grooves and encircling saidrods, and means for preventing adhesion between saidcementitiousmaterial and said rods.

3. In a concrete pipe section, reenforcing means under tension, andmeans for preventing adhesion between the reenforcing means and saidconcrete pipe section.

4. In concrete conduits and the like, reenforcement placed around theconduit in such ,a manner as to create initial compression in the.latter, and means permitting relative movement between saidreenforcement and said conduit to equalize the strain throughout thelength of the reenforcement ivvhgn the conduit is subjected to external5. In a concrete pipe section, a plurality of reenforcement membersencircling said section, means whereby initial tension is produced insaid reenforcement members, and means applied to said members tofacilitate slippage thereof relative to the concrete whereby tensilestresses from external loads will be .equally distributed throughout thelength of the reinforcement.

6. In a concrete conduit section, a. reenforcing member of dissimilarshape, means whereby an initial tension may be produced 'in thereenforcing member after the material of the concrete has partiallyhardened, and

other means provided to prevent said memj ber from becoming cement boundin the material of the conduit.

7. In a concrete pipe section, circumferentially extending grooves,reenforcing bands therein, and embedded in a yielding plastic material.

8. The method of making concrete pipe sections, which consists inmolding the pipe section with reenforcing means embedded therein so asto permit relative movement between said reenforcing means and thematerial of the wall of the pipe section, and subsequently tensioningsaid reenforcing means whereby said material is subjected to an initialcompression uniformly distributed circumferentially of the pipe section.

9. The method of making reenforced concrete pipe sections whichcomprises, treating reenforcement members to prevent the adhesion ofconcrete to said members, molding the pipe section with said memberembedded in the concrete, and subsequently placing said members undertension whereby the concrete is subjected to uniformly distributedinitial compression.

In testimony whereof, I hereunto aflix my signature.

' WALTER G. PARMLEY.

